Injection molding machines having straight hydraulic mold clamping systems are known in the art, one known system as disclosed for example in the U.S. Pat. Nos. 3,871,805 and 3,810,728 comprising a mold actuating cylinder having its piston connected to the movable mold supporting platen for moving the latter in mold opening and closing directions, and a clamp pressure booster or intensifying cylinder operative when the mold is closed to increase the fluid pressure in the mold actuating cylinder to lock the mold in closed position with force sufficient to prevent mold flashing upon injection of plasticized material thereinto.
In another known straight hydraulic clamping system such as disclosed in my co-pending application Ser. No. 483,124, filed June 26, 1974, now U.S. Pat. No. 3,941,549 granted Mar. 2, 1976 a large size clamping piston is actuated by a relatively small actuating cylinder, and during the mold closing and opening strokes, fluid flows from the clamping cylinder into a large prefill tank and vice versa, and when the mold is closed a fluid pressure operated prefill valve closes communication between the clamping cylinder and the prefill tank to trap fluid in the clamping cylinder whereby fluid under high pressure conducted into the clamping cylinder exerts the required mold locking tonnage.
In injection molding machines having straight hydraulic clamping systems of the types aforesaid, the movable mold section is clamped against a mold section mounted on a fixed platen and hence such machines do not lend themselves for insert molding in that inserts must be loaded into the mold cavity while the mold is open thereby adding to the machine cycle time.